1. Field of Invention
This invention relates to a back-extension exercising apparatus, specifically to such an apparatus which provides a broad range of resistance force adjustable by the user for back extension exercise in a portable and affordable chair format.
2. Prior Art
Low back pain is a pervasive symptom in the human population. In the U.S., a NIH study published in 1998 estimates that about one-half of adults have low back pain in any given year, and more than 26 million Americans ages 20 to 64 and almost 6 million ages 65 and older have frequent low back pain (http://www.co-cure.org/CRISP/fmsprev.htm). A literature review of multiple studies of low back pain in adults estimated that the prevalence rate among the population of North American adults is 5.6% (Loney PL and Stratford PW 1999. The Prevalence of Low Back Pain in Adults: A Methodological Review of the Literature. PHYS THER. 1999; 79:384-396); applying this estimate in today's population, approximately 18 million people are experiencing low back pain on any given day.
Most acute back pain is mechanical in nature; for example, in strained muscles; chronic low back pain is hard to diagnose and is one of the most difficult and costly medical problems in the world. The most effective way for speedy recovery from lower back pain and prevention from recurrence of the injury is exercise (“Low Back Pain Fact Sheet”, NIH Publication No. 03-5161, 2003). Studies show that strengthening exercises of low back muscles significantly improve chronic lower back pain symptoms; this improvement is long-lasting and reduces the cost for health care comparing to other more passive treatments (Carpenter, David M and Nelson, Brian W, 1999, Low back strengthening for the prevention and treatment of low back pain. Med. Sci. Sports Exerc., Vol. 31, No. 1, pp. 18-24).
The major low back muscle is erector spinae, a group of muscles and tendons that run along the lateral grooves of the vertebral column and are responsible for keeping the body in an erect position. The unique position of erector spinae makes it difficult to exercise without the assistance of special equipment. An effective strengthening exercise for the low back muscles (erector spinae) is to use a specialized back-extension apparatus. A user has his/her pelvis stabilized to the seat and pushes backwards against resistance force. Currently, those types of specialized apparatuses for the back-extension exercise are mainly available in fitness centers, which use metal blocks to produce the resistance force for the exercise. Those apparatuses are bulky, heavy and expensive. Most people, especially the ones with the most need for low back muscles exercises have limited access to this specialized apparatus.
There are a number of prior arts that described of exercising apparatus using coil springs (for example U.S. Pat. Nos. 7,381,171 and 5,110,121), however the prior arts did not provide sufficient resistance force or a selection of proper resistance force for an effective back extension exercises. In order to improve and prevent low back pain symptoms, back extension exercises using sufficient and proper level of resistance force are needed to strength the erector spinae. The proper level of resistance force for back extension exercise can vary considerably due to user's age and physical conditions. Even for same user, the resistance force used for effective exercise may increase after physical condition improves following regular exercise.
This continuation-in-part application made following improvements: the machine now uses interchangeable coil-spring cylinders as parts of resistance elements to simplify the resistance level adjustment and operation; uses constant force spring devices as alternatives within resistance elements to provide stable resistance force; adds an embodiment that use one resistance element.